First of all the simple things: Getting back the replacable parts feature of old phones.
Then context optimization: At one time I may need additional battery life, and another time I may need a second sim card.
Playing around myself: It could also become a raspberry pie with more add-ons and for the more software oriented tinkerers, and I am one of them. Playing around with the pie was always nice, but I didn't fully use it because the more creative stuff always required really working with the hardware, what I don't like at all.
Also let's not forget the Pokemon effect: If there is something that can be collected, ppl will have fun just in the collecting. And not everybody may agree but funding tech experiments by people paying for fun is a valid business model for me.
